using System;

public interface A

{

    bool validate();

}

​

public class FirstImplementation : A

{

    public virtual bool validate()

    {

        return true;

    }

}

​

public class SecondImplementation : FirstImplementation

{

    public override bool validate()

    {

        var result = base.validate();

        return false;

    }

}

​

public class Program

{

    public static void Main()

    {

        A first = new FirstImplementation();

        A second = new SecondImplementation();

        Console.WriteLine(first.validate());

        Console.WriteLine(second.validate());   

    }

}